Detection and quantitative determination of halogenated hydrocarbons in atmosphere



April 22, 1952 G. s. HAINES ET Al.

DETECTION AND QUANTITATIVE DETERMINATION OF HALOGENATED HYDROCARBONS INATMOSPHERE Filed Feb. 2e, 1945 mm e Nm 2 C Il E MSH f OED 5 NNN Ell. VAEmi SD F VWK 7 RM uw v.mubQ GF Y B Patented Apr. 22, 1952 UNITED STATESPATENT )OFFICE BETCTION AND QUANTITATIVE D ETEILIVIIi NATION OFHALOGENATED HYDROCAR- BONS IN ATMOSPHERE i George S. Haines, SouthCharleston, and Frank D. Heindel, St. Albans, W."Va.', assignors to FoodMachinery and Chemical Corporation, Wilmington, Del., a corporation ofDelaware application February 26, 1945, Serial No. 579,831 4 claims.(ci. 2135232) rhis invention relates to a process and apparatusprimarily intended for the quantitative determination oi the presence oftoxic organic halides in the atmosphere in or about manufacturing orother plants Where such atmospheres are or may be encountered.

In a number of industrial operation, methyl bromide unavoidably escapesinto the atmosphere, and since these vapors. are highly toxic, personsexposed to them in excessive concentrations, i. e., greater than 30parts per million, may develop severe symptoms of poisoning. If theexposure is prolonged, the danger to health is especially hazardous inview of the cumulative effect.

An object oi the present invention is to provide a continuous method andapparatus for the quantitative determination of methyl bromide or otherorganic halide in atmosphere likely to contain such toxic gases for thepurpose of protect- Y ing personnel against the development of hazardousconcentrations of these toxic materials. Broadly considered, the processof the present invention involves the conversion of the methyl bromideor other contaminant of the atmosphere to be tested into hydrobromio orother corresponding acid by the action cfhydrogen and heat incombination with the oxygen of the vatmosphere, then dissolving the acidformed in distilled Water or other Water of known electricalconductivity and finally measuring the conductivity of the resultingelectrolyte solution. In accordance with known principles, a measurement of the conductivity of the obtained solution by means of aconductivity cell andfconnected potentiometer or equivalent instrumentindicates the amount of electrolyte taken `from the combustion productsand hence the concentration of methyl bromide or other such compounds inthe atmosphere being tested.

More specioally, the invention contemplates a constantly operatingprocess and apparatus wherein a continuous analysis of `atmospherecontaining methyl bromide or other equivalent compound is made, in whichprocess air is withdrawn in a constant amount from the enclosure orspace containing the toxic gases and after mixing with hydrogen ispassed through a heating zone or furnace in which the mixture of gasesis heated to a high temperature and the halide converted to the halogenacid, whereupon the resulting combustion gases are mixed tvith anunvarying stream of water of Vconstant vconductivty in such manner as todissolveqall `of the acid therein, after which the resultingsolution ispassed through a conductivity cell maintained at a` constanttemperature. The conductivity'of the 'solution inthe cell is preferablyind icated on a connected potentiometer equipped to make a permanentrecord on an appropriate scale. The current in the potentiometer may beconducted through a relay to activate an alarm system whereby anyincrease in conductivity sufficient to indicate hazardous proportions oftoxic gases inthe atmospherebeing `tested causes an alarm to ring orshow.

Among the outstanding novel features of the present invention is theprocedure by which `the organic halide or other contaminant in theatmospere being tested is quantitatively converted into` the acid orother electrolyte form. The proportion of the halide or othercontaminant converted into the electrolyte form must not be variedduring the operation of the testing process, for otherwise theconductivity readings could not be accurate.` The complete conversion isobtained by mixing with the air containing the organic halide an amountof hydrogen adequate to effect or permit complete conversion of theorganic' halide in the air being tested to the corresponding hydrohalideand by heating the resulting mixture to a temperature at which theconversion vproceeds to completion.

Under Athe conditions employed in the process, the oxygen of the air,organic halide, and. hydrogen react and form hydrogen bromide, Water,and carbon oxide. 'Experimentation with various proportions of hydrogenindicates Vthat complete conversion of the' bromine content to hydrogenbromide and consistently accurate determinations can be'obtained onlyWhen the amount "of hydrogen is theoretically suilicient to react withall of the oxygen of the air introduced, Inf actual operation, `itappears desirable to use van `amount slightly in excess of thistheoretical requirement, for the possibility of error in results isthereby eliminated and experimentation has indicated that the use of anexcess does not have yany adverse effect on the operation` or therecordings obtained.

`The process and apparatus of the present inventon canbereadilyunderstood from the drawing AWhich for the most partisdiagrammatic With certain 4detailed'parts in elevation. `With referenceto the drawing, the air to be tested is Withdrawn from the space orenclosure contain ing'the contaminated atmosphere through a conduit l0by means of a vacuum pump Il at the opposite end of the apparatus. Theamount of air "drawn through the conversion apparatus of r 3 theinvention is controlled by the needle valve I2.

The hydrogen employed in the process is supplied from any suitablesource I3 as from a pressure cylinder. After passing through needlevalve I4, the hydrogen passes through a flow meter I5 into a conduit I0which joins a conduit I'I leading from a flow meter I8 in the conduitI0, the junction being in a mechanism I9 which permits mixing of thegases only at their moment of discharge. The hydrogen and contaminatedair mixture flows from this mechanism I9 inside a quartz tube suitablyof one third of an inch in diameter and mounted within an alundum tube2| or other material capable of withstanding the high temperature of thefurnace, the alundum tube suitably being one which is eight inches inlength and ve eighths of an inch in diameter. Heat is preferablysupplied to the furnace by a coil 22 connected to a source of power (notshown). The furnace is provided with a pyrometer 23 for temperaturedetermination and checking of heating conditions during continuousoperation. At its discharge end, the quartz combustion tube 20 isconnected to a conduit 24 conveying distilled water or watersubstantially free of electrolyte or of known conductivity supplied bymeans of a glass cylinder and piston solenoid actuated pump 25 in turnconnected to a source 26 of distilled water.

The problem of delivering the small stream of Water at a constant rateis most efciently solved by the use of the solenoid pump. Not only isthe delivery very constant, but the pump possesses all glass surfacesand hence does not contaminate the water. Furthermore, it isself-lubricating and requires no packing glands.

The gaseous reaction products from the furnace and the distilled waterpass through a restricted portion (e. g. 3 mm. diameter) of the tube 24and into a vertically `disposed absorber chamber 21 having acomparatively large crosssectional area (e. g. 2 cm. diameter). Thisarrangement effects rapid and complete absorption and dissolution inwater of the electrolyte in the combustion products. The unabsorbedgases leave the absorber at the top and the electrolyte solution formedtherein passes downwardly through a restricted conduit 2B connected tothe bottom end of said chamber. This conduit 28 discharges into thebottom of a conductivity cell 29 containing therein two platinizedplatinum electrodes, the platinization being accomplished suitably bythe method disclosed in Physico- Chemical Methods by Joseph Reilly etal, second edition, Van Nostrand Company, New York '1933.

After passing through the cell 29, the solution flows through theconduit 3| to the conduit 32 where it is joined by means of a valvedconduit 33 connected at its other end to the top of the chamber 21. Therecombined solution and unabsorbed gases in the conduit 32 pass to aseparator 34 from which the solution flows to a trap 35 which dischargesthe Water to waste through the overow pipe 36. The gases arising in theseparator 34 pass out through a conduit 31, the needle valve I2 and thevacuum pump II to the atmosphere.

The conductivity cell 29 is submerged in water or other liquid containedin a tank 39 adapted to maintain the temperature in the cell at anysuitable constant as for example at 40 C. Its electrodes areelectrically connected to a recorder timer 4I suitably of thepotentiometer type and CII to a relay arranged to sound an alarm, therelay and alarm being generally indicated at 42.

In the operation of the furnace, it is essential for accurate resultsthat the temperature be maintained adequately high to effect union ofall of the bromide with hydrogen. In the quartz tube furnacehereindescribed, it was found desirable at the commencement of theoperation to heat toV about 800 C. in order to obtain completeconversion of the methyl bromide to hydrogen bromide, but after thereaction had proceeded smoothly for a time, the furnace temperaturecould be decreased as low as 670 C. without causing erratic results. Forsafe operation, a furnace temperature of at least 700 C. is recommended.Temperatures as high as 1l00 C. were tried and found not to affect theaccuracy of the analyses.

The conductivity recorder :il may satisfactorily be one adapted asmanufactured to record a range of from 250 to 50,000 ohms. 1n View ofthe desirability of recording the conductivity as parts per million ofmethyl bromide in the air being tested, the recorder used by the presentapplicants was altered by replacing the ohm scale by a scale indicatingparts per million following tests and normal scale transpositionprocedure.

The conduction characteristics of the conductivity cell were firstadjusted by trimming and altering the position of the electrodes to givea desired reading on a conventional resistivity meter using a standardhydrobromic acid solution having a concentration equivalent to aselected concentration of methyl bromide. The electrodes were thensealed in a glass tube and a final calibration was made usinghydrobromic acid solutions. Finally, the cell calibration was checked bymeans of tests using methyl bromide of known concentrations. It wascalculated that if 50,000 ohms represented one part per million ofmethyl bromide in the atmosphere, then 250 ohms on the scale indicated amethyl bromide concentration of parts per million. With the new scale inplace, the test run conducted on a known methyl bromide concentrationpermitted adjustment of the substituted scale to obtain a correctreading. The electrodes employed were composed of platinized sheets ofplatinum foil 0.0025 inch .in thickness and were mounted approximately 2mm. apart by means of two glass spacers and were sealed with platinumlead wires in a glass tube of 16 mm. diameter.

Using the above-described apparatus, it was ascertained on test that allvariations of the methyl bromide concentration above about 15 parts permillion up to 600 were consistently within about five per cent of theactual concentrations. .If for any reason greater accuracy is desired ateither higher or lower concentrations, this objective could be easilyobtained by altering the size of or the distance between the electrodes,by altering the rate of air flow, by altering the rate of Water flow, orby making any combination of these alterations.

In a typical operation in the apparatus herein-described, air containingmethyl bromide was passed into the apparatus at the rate of 1000 ml. perminute and the hydrogen at the rate of 420 ml. per minute. This mixturewas then run through the furnace and heated to a temperature of 700 C.The reaction products were then mixed with distilled water introduced atthe rate of 10 Inl. per minute and the resulting solution passed throughthe conductivity cell of the structure hereinbefore described.

The apparatus of the present invention is parpounds of nitrogen. Theapparatus may also jbe i effectively employed for locating leaks incontainers in `equipment which contains volatile 4or gaseous poisonouscompounds When chlorine-.compounds and certain other of the mentionedcompounds but not those of brornine and iodine are treated in theapparatus, the flow of hydrogen maybe wholly or in part dispensed withand 'water vapor substituted therefor. This water-may be-supplied by.Cutting into the air conduit I1 the jacketed tank ,43 into which theair is introduced-below the surface of water contained therein. Theamount of moisture taken up is controlled simply by regulation of thetemperature of the water and saturation of the air with moisture. Whenchlorine compounds or other similarly reacting compounds are treated,the introduction of suicient moisture into the air avoids the occurrenceof free chlorine in the combustion products by causing quantitativeformation of hydrogen chloride.

Since the present apparatus is not restricted to the detection anddetermination of methyl bromide concentrations, the presence of theother contaminants of the nature above described will also be detectedby causing an increase in conductivity, and an additional safety factoris provided.

In the use of the process and apparatus of the present invention, it iscontemplated that air be withdrawn for testing from several differentsources or points where contamination is likely to occur. Since it isdesirable that individual recordings be made for the tests on theatmosphere from the several sources, much of the apparatus must beduplicated for each source tested. However, any number of combustiontubes may be combined in one furnace and any number of absorberconductivity cells may be immersed in one temperature regulating bath.Furthermore, a single vacuum pump operating through a manifold can beconnected to any number of conduits for the discharge of gases from theseparator and one trap may likewise be used for the discharge of thetested liquid from the separator. Finally, one conductivity recorder ofthe six point variety can be employed for the simultaneous testing ofsix solutions from six sources of contaminated air.

It should be understood that the present invention is not limited to thespecific details of construction or procedure herein described but thatit extends to all equivalents which will occur to those skilled in theart upon consideration of the scope of the claims appended hereto.

We claim:

l. A process for quantitatively determining the presence of halogenatedhydrocarbons including bromides, chlorides and iodides in an atmospherecontaminated with the same, which comprises adding to such contaminatedair an amount of hydrogen gas theoretically sufficient to react with theoxygen content of the atmosphere in excess of that part thereof whichwill react with` the halogenated hydrocarbon therein, heating theresulting mixture to an ,elevated temperature and by the aid of suchheat. (l) con# verting the halogenated hydrocarbons into hydrogenhalides through reaction with oxygen in the air, and 2) reacting theadded hydrogen present with the remaining oxygen whereby the formationof free halogen is prevented, dissolving the hydrogen halides formed inwater of known electrical conductivity and measuring the electricalconductivity of the resulting solution.

2. A process for quantatively determining the presence of brominatedhydrocarbons in an atmosphere contaminated with the same, comprisesadding to such contaminated air an amount of hydrogen gas theoreticalysuiicient to react With the oxygen content of the atmosphere in excessof that part thereof which will react with the brominated `hydrocarbonstherein, heating the resulting mixture to an elevated temperature and bythe aid of such heat, (1) converting the brominated hydrocarbons into hydrogen bromide through reaction with oxygen in the air, and (2) reactingthe added hydrogen present with the remaining oxygen whereby theformation of free bromine is prevented, dissolving the hydrogen bromideformed in water of known electrical conductivity and measuring theelectrical conductivity of the resulting solution.

3. A process for quantitatively determining the presence of methylbromide in an atmosphere contaminated with the same, which comprisesadding to such contaminated air an amount of hydrogen gas theoreticallysuicient to react with the oxygen content of the atmosphere in excess ofthat part thereof which will react With the methyl bromide therein,heating the resulting mixture to an elevated temperature and by the aidof such heat, (l) converting the methyl bromide into hydrogen bromidethrough. reaction with oxygen in the air, and (2) reacting the addedhydrogen present with the remaining oxygen whereby the formation of freebromine is prevented, dissolving the hydrogen bromide formed in water ofknown electrical conductivity and measuring the electrical conductivityof the resulting solution.

4. A continuous process capable of quantitatively determining thepresence of halogenated hydrocarbons including bromides, chlorides andiodides in an atmosphere which comprises, conducting a constant streamof air from the atmosphere to be tested together with a stream ofhydrogen in an amount theoretically suilicient to react with the oxygencontent of the air in excess of that part thereof which will react withthe halogenated hydrocarbon therein, through a hating zone at atemperature which (1) converts the halogenated hydrocarbons intohydrogen halides through reaction with oxygen in the air and (2) reactsthe added hydrogen present with the remaining oxygen whereby theformation of free halogen is prevented, passing the reaction productsobtained containing the hydrogen halide into a constant stream of waterof constant conductivity whereby said acid goes into solution,continuously passing said solution through a conductivity cell andconstantly measuring the conductivity imparted by the halide, therebydetermining variations in the organic halide content of the atmosphere.

GEORGE S. I-IAINES. FRANK D. HEINDEL.

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1. A PROCESS FOR QUANTITATIVELY DETERMINING THE PRESENCE OF HALOGENATEDHYDROCARBONS INCLUDING BROMIDES, CHLORIDES AND IODIDES IN AN ATMOSPHERECONTAMINATED WITH THE SAME, WHICH COMPRISES ADDING TO SUCH CONTAMINATEDAIR AN AMOUNT OF HYDROGEN GAS THEORETICALLY SUFFICIENT TO REACT WITH THEOXYGEN CONTENT OF THE ATMOSPHERE IN EXCESS OF THAT PART THEREOF WHICHWILL REACT WITH THE HALOGENATED HYDROCARBON THEREIN, HEATING THERESULTING MIXTURE TO AN ELEVATED TEMPERATURE AND BY THE AID OF SUCHHEAT, (1) CONVERTING THE HALOGENATED HYDROCARBONS INTO HYDROGEN HALIDESTHROUGH REACTION WITH OXYGEN IN THE AIR, AND (2) REACTING THE ADDEDHYDROGEN PRESENT WITH THE REMAINING OXYGEN WHEREBY THE FORMATION OF FREEHALOGEN IS PREVENTED, DISSOLVING THE HALOGEN HALIDES FORMED IN WATER OFKNOWN ELECTRICAL CONDUCTIVITY AND MEASURING THE ELECTRICAL CONDUCTIVITYOF THE RESULTING SOLUTION.